Surgical instruments

ABSTRACT

A connector for use in orthopaedic surgery for location of a surgical instrument relative to a reference point, comprises a plate member ( 30 ) having a reference point which can be fastened to the bone, and a connector rod ( 32 ) for connecting the surgical instrument ( 56 ) to the plate member. The connector rod is pivotally connected ( 44 ) to the plate member at about the reference point allowing relative pivotal motion between the connector rod and the plate member around at least one axis ( 46 ).

This invention relates to instruments for use in orthopaedic surgery,including an instrument for location of a reference point relative to abone surface, and a connector for location of a surgical instrumentrelative to a reference point.

Instruments are used in orthopaedic surgery for location of instrumentssuch as drills, saws, reamers and the like, to optimise the accuracy ofsubsequent steps in a surgical procedure using those instruments. Forexample, an instrument can be used to define an axis relative to a bone,along which a cavity in the bone is subsequently prepared using toolssuch as drills and reamers. Instruments for use in such location stepsshould enable satisfactory accuracy to be achieved. They should minimisetrauma to the patient and, in particular, minimise disturbance of tissuewhich would not otherwise be affected by the surgical procedure.

U.S. Pat. No. 5,766,263 and U.S. Pat. No. 6,120,544 relate to a femoralcomponents of artificial hip joints which are mounted in the upperregion of the femur below the greater trochanter, within and alignedwith the femoral neck axis. These components can be contrasted withwidely used hip joint femoral components which extend into theintramedullary cavity extending along the femur axis. Use of thecomponents with which U.S. Pat. No. 5,766,263 and U.S. Pat. No.6,120,544 are concerned has the advantage that less of the patient'snatural bone tissue is removed during surgery: the bone is resected onthe femoral neck, just below the spherical head, rather than by removalof the entire head section of the femur, including the greatertrochanter by resection in the metaphysial region. In addition, thelength of the incision that is required is smaller than withconventional implants. The procedure for implanting a prosthesis of thekind disclosed in U.S. Pat. No. 5,766,263 and U.S. Pat. No. 6,120,544 istherefore less traumatic for the patient. The resection of less boneallows better for the possibility of revision surgery at a later date inthe event that the original prosthesis implantation fails.

The prostheses disclosed in U.S. Pat. No. 5,766,263 and U.S. Pat. No.6,120,544 are implanted on the axis of the femoral neck. Preparing thebone for the implantation requires accurate location of the neck axis.This is also important because the resection plane should generally beorthogonal to this axis. The axis can be defined by locating a point onthe lateral cortex which lies opposite to the centre of the femoralhead, where the axis intersects the cortex. This can be identifiedduring pre-operative planning, for example using X-ray or other imagesof the femur, in particular relative to prominent landmarks on the bonesurface. In the case of the prosthesis disclosed in U.S. Pat. No.5,766,263, a hole is formed in the lateral cortical tissue for a draw-inscrew, by which a shell part introduced into the femur through theresected femoral neck is drawn into the bone. The hole can be formed bya drill after resection of the bone, extending through the femur, alongthe neck axis. Drill guides which enable accurate location of the neckaxis for drilling from the lateral surface to the medial surface areknown. They have the disadvantage that they require exposure of thepoint on the lateral cortical bone at which the axis intersects thatbone, involving in particular the displacement of muscle and other softtissue.

In the case of the prosthesis disclosed in U.S. Pat. No. 6,120,544, thefemur remains intact in the region of the lateral cortex opposite to theresected femoral neck. The prosthesis is inserted into a prepared cavityin the bone, and acts against the lateral cortical bone tissue, and thefact that the tissue remains intact helps it to withstand the loadstransmitted on to it when the prosthesis is placed under load. However,there remains a need to locate the neck axis accurately when preparingthe cavity for implantation of a femoral component.

In one aspect, the invention provides a connector for use in orthopaedicsurgery for location of a surgical instrument relative to a referencepoint, which comprises a plate member having a reference point which canbe fastened to the bone, and a connector rod for connecting the surgicalinstrument to the plate member, the connector rod being pivotallyconnected to the plate member at about the reference point allowingrelative pivotal motion between the connector rod and the plate memberaround at least one axis.

The instrument of the invention allows a reference point to beestablished relative to a bone surface without direct access to the bonesurface at that point, for example for fastening the instrument to thebone. This can be important when soft tissue, especially muscle tissue,overlies the bone surface at the intended reference point which wouldhave to be displaced if the plate member is to be fastened to the bonesurface using fasteners inserted into the bone at or close to thereference point. The instrument of the invention therefore provides forlocation of a reference point accurately and closely relative to a bonesurface, and fixation to the bone surface, without disturbing softtissue which overlies the bone at the reference point.

The connector rod can be used for mounting an instrument which is usedduring preparation of the bone for implantation of a prosthesiscomponent. Examples of such instruments include drills, saws, reamersand the like. The instrument might also be a locator for a sleeve whichis fastened to the resected femoral neck to define the neck axis. Theinstrument of the present invention allows the orientation of suchinstruments to be controlled relative to the reference point defined bythe plate member.

Preferably, the plate member has at least two holes in it towards oneend for receiving fasteners which can pass through the holes into thebone to fasten the plate member to the bone, a pivot rocker between thesaid holes which protrudes from the face of the plate member which facesthe bone surface when the plate member is positioned against a bone. Thereference point can be located towards the opposite end of the platemember from the fastening holes, spaced from the fastening holes in adirection parallel to the line which intersects the holes, in which thedistance between the reference point on the plate member and the surfaceof the bone can be adjusted by moving the fastener in one of thefastening holes into the bone and moving the fastener in the other ofthe fastening holes out of the bone.

The instrument of the invention has the advantage that it allows areference point to be located relative to a bone surface using a platemember which is fastened to the bone remote from the reference point. Inparticular, the nature of the fixation of the plate member to the bonesurface using two (or more) fixation holes with a pivot rocker betweenthem means that the distance between the plate and the bone at thereference point can be adjusted. This can be important when it isimportant for the reference point to be located as close as possible tothe bone surface, for example when defining an axis which passes throughthe bone surface at a previously identified location (corresponding asclosely as possible to the location of the reference point on the platemember).

The location of the plate member relative to the bone can be performedusing data from pre-operatively generated images, in particular byidentifying appropriate landmarks on the bone surface relative to theappropriate location of the plate member.

Preferably, the relative pivotal motion of the connector rod relative tothe plate member is such that the connector rod can be pivoted about anaxis which extends roughly parallel to the axis of the bone. This canhave considerable advantages in terms of minimising the size of theincision that is necessary during preparation of a bone for implantationof a prosthesis. For example, the instrument of the present inventioncan be fastened to a bone laterally using the fastening holes in theplate member, with the connector rod located outside the incision, andthe region of the bone that is exposed including only (a) the intendedlocation of the reference point, and (b) the bone surface into which thefasteners (for example screws) are to be inserted. An axis whichincludes the reference point can then be defined by rotating the bonearound its axis relative to the incised soft tissue, pivoting theconnector rod relative to the affixed plate member.

Preferably, the connector rod has an arcuate shape so that it can extendaround the bone from the bone surface against which the reference pointis located to an opposite bone surface to define an axis which extendsbetween the two surfaces.

Preferably, the connection between the connector rod and the platemember permits relative pivotal motion about at least two axes, andpossibly about three axes for some applications. When the connector rodand plate member can pivot about two axes, they will often beorthogonal. However, other arrangements might be appropriate for someapplications.

The connector rod can include a mount at its end remote from theconnection to the plate member for another instrument component, forexample such as a saw, reamer or drill. When the connection between theconnector rod and the plate member permits relative pivotal motion aboutat least two axes, the mount for the other instrument component canallow the component to be pivoted relative to the connector rod aroundan axis which is orthogonal to each of the axes of rotation of theconnector rod relative to the plate member.

The mount can includes a track on which the surgical instrument canslide relative to the connector rod, so that the connector rod can bemoved pivotally relative to the reference point without a significantchange in the position of the instrument. Preferably, the track isarcuate, especially with a radius approximately equal to the distancefrom the track to the reference point on the plate member. This allowsthe connector rod to be moved pivotally relative to the plate member sothat the connector rod can be fitted close to the bone to which theplate member is fastened. This has the significant advantage of enablingthe size of the incision to be kept small while accommodating theinstrument during the procedure, and also enabling the instrument to beused on patients with relatively bones.

It can be preferred for the connector rod to comprise at least twomodules, so that the configuration of the connector rod can be changedby replacement of one of the modules. For example, one module can beprovided in a plurality of variants, for example with different lengths,allowing the length of the connector rod to be changed.

The connector rod can carry a scale for indicating where the bone shouldbe resected. The rod might have a cutting edge to facilitate marking thebone. A scale can also be provided on a module of a connector rod whichcan be replaced by another module after the location of the resectionhas been determined.

The reference point has been discussed above as the point at which aconnector rod is connected to the plate member. It could be marked onthe plate member in other ways. For example, the plate member could havea guide hole at the reference point, for example for receiving a drillby which a hole can be formed in the bone at the reference point. Itmight also be marked in other ways such as by the location of a markerwhich is designed to be visible using an appropriate scanningtechnology. For example, a tantalum marker can be used to locate areference point so that it is visible using X-ray scanning technology.

The pivot rocker protrudes from the face of the plate member which facesthe bone surface when the plate member is positioned against a bone, ata point between the holes for the fasteners. The rocker will often belocated so that the pivot point is roughly equidistant from the twoholes. The rocker can be configured so that it defines a ridge extendingroughly perpendicular to a line which intersects the two fasteningholes, and generally parallel to the plane of the plate member (when itis planar). The height of the ridge will depend on, amongst otherthings, the shape of the bone on which the plate is to be used, thedistances between the pivot rocker and the fixation holes, and thedistance between the pivot rocker and the reference point. For someapplications, the height of a suitable ridge will be at least about 2mm, preferably at least about 4 mm. The distance between the fixationholes can be at least about 15 mm, preferably at least about 25 mm. Thedistance from the pivot rocker to the reference point can be at leastabout 25 mm, preferably at least about 30 mm. The distance from thepivot rocker to the reference point can be not more than about 40 mm,preferably not more than about 35 mm.

The fixation holes can be countersunk. This has the advantage thatfasteners such as screws can be recessed within the holes, reducing therisk of damage to tissue when the device is moved relative to overlyingtissue.

Preferably, the reference point lies on the line which intersects thefastening holes. However, for some configurations of plate members, thereference point will be spaced from the fastening holes in a directionparallel to that line, but displaced from that line to one side orother. Preferably, the distance between the fastening holes is less thanthe distance between the reference point and the fastening hole that isnearer to it, measured along the line which intersects the fasteningholes or a line extending parallel to it.

The plate member will be configured having regard to the configurationof the bone surface on which it is to be used. When the bone surface isgenerally flat (at least over that part with which the plate membercomes into contact), the plate member can be generally flat, apart ofcourse from the pivot rocker. However, the bone surface (together withany associated overlying soft tissue) will often not be flat. Forexample, when the invention is intended to be used to locate the lateralend of the femoral neck axis, the relevant lateral surface of the bonehas an overlying layer of muscle. It is also concave. It can thereforebe appropriate for the plate member to have an arcuate configuration sothat it generally follows the shape of the bone on to which it is to befitted when the instrument is in use.

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIG. 1 is an isometric view of a known instrument which is used todefine the neck axis of a femur in order to prepare the femur forimplantation of a prosthetic joint component.

FIG. 2 is an isometric view of an instrument according to the presentinvention.

FIG. 3 is a side view of the instrument shown in FIG. 2, along the lineindicated by the arrow III.

FIG. 4 is an end view of the instrument shown in FIG. 2, along the lineindicated by the arrow IV.

Referring to the drawings, FIG. 1 shows a femur 2 which has beenresected in the neck region 4 below the spherical head. The greatertrochanter 6 remains intact as a result of this resection.

The femoral neck has to be prepared by creation of a cavity along theaxis of the neck, into which the femoral of a hip joint prosthesis canbe inserted. The axis is located by determining the point 8 on thelateral cortical bone tissue where the axis intersects the corticalbone. This can be done with reference to pre-operation scan images ofthe patient's bone. A drill guide 10 can be fixed relative to the point8 on the cortex using a sleeve 12 which is fastened to the bone. Theother end 14 of the axis is determined by visual inspection of theresected femur.

The instrument shown in FIG. 1 can then be used to prepare an axialbore, using a drill 16 in conjunction with the drill guide 10. One arm20 of the drill guide is positioned against the resected femur, and thedrill guide extends around the bone to intersect the axis on the lateralside of the bone where it engages the sleeve 12, allowing the guide thento be used to locate the drill as it is inserted into the bone tissue.

The drill guide arrangement shown in FIG. 1 has a number ofdisadvantages. In particular, a large incision is required in order toexpose the bone sufficiently. In addition, in order to fasten the sleeve12 onto the lateral cortical bone by means of a fixation plate 22, andalso to drill into that bone, it is necessary to strip away muscle andother tissue which overlies the bone in this region. This complicatesthe surgical procedure and can delay or prevent full recovery by thepatient.

The device of the present invention is shown in FIGS. 2 to 4. Itcomprises a plate member 30, a connector rod 32, and a mount 34 for asurgical instrument. The plate has two fastening holes 36, 38 towardsone end, with a pivot rocker 40 protruding from the surface 42 whichfaces towards the bone when the device is in use. The plate member isslightly curved so that it can follow the concave shape of the femur onthe lateral face below the greater trochanter.

The plate member is connected by means of a joint to the connector rod32 at the end of the plate member 30 opposite to the fastening holes.The connection is made by means of a universal joint 44 which allows theconnecting rod to be pivoted relative to the plate member about twoorthogonal axes 46, 48. One of those axes 46 is aligned approximatelywith the axis of the femur, at least so that the connector rod can bepivoted around the femoral axis.

The connector rod 32 is provided in two modules 50, 52. The first module50 is connected to the plate member by means of the universal joint. Thesecond module 52 can be replaced by other second modules with differentlengths in order to vary the effective rod of the connector rod. Theconnection between the modules can be provided by means of a press-fit,spigot and socket arrangement, for example with a spring loaded stud anddetent arrangement to prevent inadvertent separation. The second modulemight have other functions other than to bear a instrument mount. Forexample, it might include a scale to enable a surgeon to judge where thebone should be resected for receiving the implant. The module might havea cutting edge to facilitate marking the bone. A scale can also beprovided on a connector rod which is not modular.

The connector rod 32 has a mount 34 at the end remote from the platemember for mounting a surgical instrument such as a drill or a reamer,or a manipulator 56 (as shown) for a sleeve 57 which will define thefemoral neck axis, and into which a drill can be inserted to create theneck bore. The manipulator 56 includes a handle 58. The sleeve with theoverlying handle are hollow so that a drill or reamer or other tool canbe inserted into the sleeve. The mount is arranged on the connector rodso that it can be pivoted relative to the end of the rod. The axis aboutwhich the mount can be pivoted is orthogonal to the two axes 46, 48about which the connecting rod can be pivoted relative to the platemember.

The mount 34 comprises a track which the sleeve 57 can be slid along,along a line in the plane of the page on which FIG. 3 is shown. Thetrack is arcuate with a radius approximately equal to the distance fromthe track to the reference point on the plate member. This allows theconnector rod 32 to be moved pivotally relative to the plate member sothat the connector rod can be fitted close to the bone to which theplate member is fastened. This has the significant advantage of enablingthe size of the incision to be kept small while accommodating theinstrument during the procedure, and also enabling the instrument to beused on patients with relatively bones.

In use, a patient's femur is prepared by incision to expose the femur inthe region of the lateral cortex. It is possible for the length of theincision to be kept as low as about 60 mm. Previously generated scannedimages enable the location of the intersection of the femoral neck axiswith the lateral cortex (the “target point”) to be identified. The platemember 30 is then fixed to the femur at a location remote from thetarget point, in a direction towards the greater trochanter. It is fixedby means of bone screws which are inserted into the femur through thefixation holes 36, 38. The tension that is applied to the screws iscontrolled so that the universal joint 44 at the opposite end of theplate member is located as close as possible to the target point on thelateral cortex. It will be understood that the bone itself in thisregion is covered with muscle and other tissue. The provision of thepivot rocker with a fixation screw on each side allows the orientationof the plate member relative to the bone surface to be adjusted so thatthe universal joint end of the plate member is located as close aspossible to the muscle. In contrast with the known device shown in FIG.1, it is not necessary with the device of the invention to expose thebone at the target point in order to achieve appropriate fixation of theinstrument relative to the target point.

The bone can then be rotated relative to the site of the incision,feeding the connector rod 50 around the bone so that, when the resectedfemoral neck is exposed, the guide arm extends around the bone and thesleeve 57 is mounted above the resected neck. The orientation of thesleeve (degree of anteversion) can be adjusted by manipulation of themount relative to the connector rod, according to the surgeon'sjudgment. The mount can include a scale to indicate the degree ofanteversion that is applied to the instrument. The sleeve can then beused to prepare a cavity in the femur for the femoral component of a hipjoint which is intended to be implanted generally in line with thefemoral neck axis.

The instrument of the invention has the advantage that disruption tomuscle and other soft tissue attached to a bone can be minimised byremote fixation of a location device. In addition, the size of theincision for implantation of the joint prosthesis need not be enlargedrelative to the size that is necessary to insert the implant theprosthesis itself, in order to accommodate the instrumentation used toprepare the bone for the implantation.

1. A connector for use in orthopaedic surgery for location of a surgicalinstrument relative to a reference point, which comprises a plate memberhaving a reference point which can be fastened to the bone, and aconnector rod for connecting the surgical instrument to the platemember, the connector rod being pivotally connected to the plate memberat about the reference point allowing relative pivotal motion betweenthe connector rod and the plate member around at least one axis.
 2. Aconnector as claimed in claim 1, in which the plate member has at leasttwo holes in it towards one end for receiving fasteners which can passthrough the holes into the bone to fasten the plate member to the bone,a pivot rocker between the said holes which protrudes from the face ofthe plate member which faces the bone surface when the plate member ispositioned against a bone.
 3. A connector as claimed in claim 1, inwhich the connector rod is pivotally connected to the plate member atabout the reference point to allow relative pivotal motion between theconnector rod and the plate member around at least two axes.
 4. Aconnector as claimed in claim 1, in which the connector rod has anarcuate shape so that it can extend around the bone from the bonesurface against which the reference point is located to an opposite bonesurface to define an axis which extends between the two surfaces.
 5. Aconnector as claimed in claim 1, in which the connector rod includes amount at its end remote from the connection to the plate member for asurgical instrument.
 6. A connector as claimed in claim 4, in which theconnector rod is pivotally connected to the plate member at about thereference point so as to allow relative pivotal motion between theconnector rod and the plate member around at least two axes, and inwhich the mount allows the instrument to be pivoted relative to theconnecter rod around an axis which is orthogonal to each of the axes ofrotation of the connector rod relative to the plate member.
 7. Aconnector as claimed in claim 4, in which the mount includes a track onwhich the surgical instrument can slide relative to the connector rod,so that the connector rod can be moved pivotally relative to thereference point without a significant change in the position of theinstrument.
 8. A connector as claimed in claim 1, in which the connectorrod comprises at least two modules, so that the configuration of theconnector rod can be changed by replacement of one of the modules.
 9. Aconnector as claimed in claim 7, in which one of the modules includesthe plate member, and in which the other module bears at least one of(a) a mount for a surgical instrument, and (b) a scale for indicatingwhere the bone should be resected.